Kinetics of n-butoxy and 2-pentoxy isomerization and detection of primary products by infrared cavity ringdown spectroscopy

The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O(2) have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O(2) were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν(1)) absorption spectra for δ-HO-1-C(4)H(8)?, δ-HO-1-C(4)H(8)OO?, δ-HO-1-C(5)H(10)?, and δ-HO-1-C(5)H(10)OO?. The observed ν(1) bands are similar in position and shape to the related alcohols (n-butanol and 2-pentanol), although the HOROO? absorption is slightly stronger than the HOR? absorption. We determined the rate of isomerization relative to reaction with O(2) for the n-butoxy and 2-pentoxy radicals by measuring the relative ν(1) absorbance of HOROO? as a function of [O(2)]. At 295 K and 670 Torr of N(2) or N(2)/O(2), we found rate constant ratios of k(isom)/k(O(2)) = 1.7 (±0.1) × 10(19) cm(-3) for n-butoxy and k(isom)/k(O(2)) = 3.4(±0.4) × 10(19) cm(-3) for 2-pentoxy (2σ uncertainty). Using currently known rate constants k(O(2)), we estimate isomerization rates of k(isom) = 2.4 (±1.2) × 10(5) s(-1) and k(isom) ≈ 3 × 10(5) s(-1) for n-butoxy and 2-pentoxy radicals, respectively, where the uncertainties are primarily due to uncertainties in k(O(2)). Because isomerization is predicted to be in the high pressure limit at 670 Torr, these relative rates are expected to be the same at atmospheric pressure. Our results include corrections for prompt isomerization of hot nascent alkoxy radicals as well as reaction with background NO and unimolecular alkoxy decomposition. We estimate prompt isomerization yields under our conditions of 4 ± 2% and 5 ± 2% for n-butoxy and 2-pentoxy formed from photolysis of the alkyl nitrites at 351 nm. Our measured relative rate values are in good agreement with and more precise than previous end-product analysis studies conducted on the n-butoxy and 2-pentoxy systems. We show that reactions typically neglected in the analysis of alkoxy relative kinetics (decomposition, recombination with NO, and prompt isomerization) may need to be included to obtain accurate values of k(isom)/k(O(2)).     

Statistical equilibrium solutions of the shallow water equations

A statistical method for calculating equilibrium solutions of the shallow water equations, a model of essentially 2D fluid flow with a free surface, is described. The model contains a competing acoustic turbulent direct energy cascade, and a 2D turbulent inverse energy cascade. It is shown, nonetheless that, just as in the corresponding theory of the inviscid Euler equation, the infinite number of conserved quantities constrains the flow sufficiently to produce nontrivial large-scale vortex structures which are solutions to a set of explicitly derived coupled nonlinear partial differential equations.     

Critical dynamics of the dirty boson problem: revisiting the equality z=d

It is shown that previous arguments, leading to the equality z=d for the dynamical exponent describing the Bose glass to superfluid transition in d dimensions, may break down, as apparently seen in recent simulations. The key observation is that the major contribution to the compressibility, which remains finite through the transition and was predicted to scale as kappa approximately |delta|((d-z)nu) (where delta is the deviation from criticality and nu is the correlation length exponent) comes from the analytic, not the singular part of the free energy, and is not restricted by any conventional scaling hypothesis.     

Excitation characteristics of the IR luminescence in CU2O

Detailed luminescence excitation characteristics of the long-wave (0.93 μm), medium-wave (0.82 μm), and short-wave (0.72 μm) emission peaks in cuprous oxide were studied under pulsed dye laser excitation. The results show that the emission spectrum at 193 K contains only two peaks at 0.93 and 0.72 μm for excitation wavelenghts less than 5800 Å, and that for excitation wavelengths 5800 Å and longer an emission peak also appears at 0.82 μm. This medium wave band increases relatively faster with increase in wavelength until it becomes the dominant luminescent peak at an excitation wavelength of 6350 Å. All three emission peaks have much narrower excitation curves at 300 K than at 77 K, with the peak excitation wavelength shifting to longer wavelengths at higher temperature.